1. Field of the Invention
The present invention relates generally to an improvement in a glass heat treatment furnace such as an annealing furnace or a roller hearth furnace in which glass is subjected to heating or cooling while being transferred, and more particularly to a supporting structure for a plurality of roller supporting units aligned in the direction of the glass being transferred, each unit consisting of a plurality of parallely and spacedly arranged rollers for glass transferring, or for a plurality of bed units aligned in the same direction so that glass is transfered under assistance of gas layer, the bed units being, for example, hearth beds of a gas hearth furnace which beds are aligned in the glass transferring direction so that glass is heated to be bent.
2. Description of the Prior Art
In connection with, for example, conventional gas hearth furnaces, a support structure for each hearth bed consists of refractory support blocks disposed at the opposite sides of the bottom surface of the hearth bed. Each support block covered with a support frame made of stainless steel. Additionally, vertically standing support pillars are provided to support the bed at its four corners through the support block and frame. Each support pillar is made of metal and stands on a support stand which is provided with a device for adjusting the vertical location of the hearth bed. Thus, the supporting structure for the hearth bed is generally constructed of members made of metal and usual refractory.
Now, in order precisely bend a plate glass along the upper curved surface of the hearth bed of the thus arranged conventional gas hearth furnace, it is preferable that the clearance between the adjacent hearth beds is not larger than 1 mm and the difference in level of the top surfaces amoung the aligned hearth beds is not larger than 0.5 mm. However, the above-mentioned hearth bed structure consists of the metallic support pillars which have a high coefficient of thermal expansion, and therefore considerable differences in expansion length unavoidably occur among the support pillars due to temperature distribution in the furnace so that the support pillars are respectively heated at different temperatures upon operation of the furnace. This results in differences in level of the top surfaces among the aligned hearth beds even though the top surfaces of the hearth beds are adjusted to be brought into alignment with each other by means of the vertical location adjusting device at a low temperature before operation of the furnace. In this regard, it becomes necessary to precisely adjust the vertical location of the hearth beds at high temperatures during operation of the furnace. Such location adjustment at high temperatures is troublesome and requires much labor and much time, thereby lowering productivity of glass products.